The Tepee Buttes (~76 Ma, Campanian) of Colorado provide an excellent opportunity to model the preserved record of geomicrobial processes at a fossil methane seep at a scale that has not been realized. The broad aerial extent, accessibility, and quality of preservation allow for the development of a genetic model of carbonate precipitation over time at individual seeps and throughout the entire field. As the precipitation is mediated by both anaeorobic oxidation of methane (AOM) and bacterial sulfate reduction (BSR), the geologic record serves as a proxy for how the localized microbial ecosystems vary temporally and spatially through the life cycle of an individual seep. This proposal seeks to address the depth within the sediment at which carbonate production occurs, to quantify whether the carbonate produced from localized microbial ecosystems differs geochemically and petrographically from carbonate associated with chemosymbiotic invertebrates, and to model how the biogeochemical parameters vary in time and space.
Preliminary work on the Tepee Buttes has demonstrated that the complex paragenetic sequence of petrofabrics will, along with the stable isotopic ratios, be useful in developing a model of the formation of the carbonate mounds, including depth of formation. The recognition of bacterial body fossils and microbialite will allow us to map the adjustment of localized microbial ecosystems over the lifecycle of each butte. Carbon and oxygen stable isotope analyses have shown that there is variation among sequences between buttes and we will address these phenomena. The PIs propose to address the temporal and spatial sequencing of the microbially induced carbonate/sulfide production through a collaborative project involving two undergraduate institutions (Gustavus Adolphus and Oberlin Colleges) and a major research university (University of Missouri, Columbia). The research entails detailed field mapping over an approximately 3 km2 area, taphonomic and petrographic study, and isotope geochemistry. In the field, surface components of the mounds will be mapped to demonstrate microbial ecosystem distribution in relation to carbonate phases and invertebrate populations. In the laboratory, we will build upon earlier successes by applying a multi-directed analytical approach involving petrography (cathodoluminescence, x-ray fluorescence), SEM/EDS, and stable isotope ratios (C, O, and S).
Intellectual Merit. Knowledge of the genesis of the Tepee Buttes will provide important tools for defining microbial-sediment interactions in modern and ancient seep settings.an active research area for (paleo) biologists, geologists, and geophysicists. By applying a collaborative approach, the PIs will gain from the individual strengths in microbial paleontology, taphonomy, and isotope geochemistry focused on refining biogeochemical proxies for recognizing the fossil record of microbial ecosystems. Broader Impacts. The results of this project will be valuable to researchers studying biogeochemical patterns at both fossil and modern methane seeps. The dissemination plan calls for the development of a DVD/CD-ROM for educators that will open up the dynamic and complex world of microbial-sediment interactions in methane seeps to a broad audience. This research will provide critical primary research experience for at least four undergraduate students who will be involved in all aspects of the research including formulation of field strategy, laboratory analysis, and preparation of manuscripts. The students will gain an appreciation for collaboration through the experience and teaching workshops, and the project will broadly impact the undergraduate research capabilities and teaching pedagogies of the PIs.
